1. Field of the Invention
The present invention relates to a heat treatment apparatus such as a heater or a pre-heater to be assembled in a semiconductor manufacturing system for manufacturing semiconductor elements by use of a photomechanical process, for instance.
2. Description of the Related Art
Conventionally, in a semiconductor manufacturing system which employs a photomechanical process, various kinds of treatment units such as a resist coating unit, a drying unit, a heating unit and the like are assembled in one system. And, a string of treatments are carried out while transferring among these various kinds of treatment units in turn.
FIG. 12 shows a vertical cross section of a typical heat treatment unit 500.
In this heat treatment unit 500, a semiconductor wafer (hereinafter simply refers to as "wafers") W is disposed on an upper surface of a heat treatment table 501, and the wafer W is heated by heat evolved from the heat treatment table 501. In this heat treatment table 501, a heating mechanism which is not shown in the figure is integrated, the heat treatment table 501 is heated by heat supplied from this heating mechanism. On the upper surface of the heat treatment table 501, there are disposed a plurality of small projections which are not shown in the figure, the wafer W is disposed on the tops of these small projections, thus the lower surface of the wafer W is designed to be prevented from being scratched or stuck by dust due to contact between the lower surface of the wafer W and the upper surface of the heat treatment table 501. Therefore, between the lower surface of the wafer W and the upper surface of the heat treatment table 501, minute gaps are formed, and, from the upper surface of the heat treatment table 501, heat is supplied to the lower surface of the wafer W through a gas, for instance, a nitrogen gas in the gaps. The gas heated by the heat treatment table 501 and the wafer W, being smaller in its specific gravity than that of the surrounding air of lower temperature, ascends within the heat treatment unit 500, is collected in a cover assembly 502 disposed oppositely above the heat treatment table 501, and is evacuated through a piping 504 connected to the top 503 of the cover assembly 502.
Now, an wafer W is liable to be affected by heat. Thus, when the heat treatment temperature goes out of its allowed range, the quality of the semiconductor products deteriorates to lead to a lower yield, resulting in an increase of the manufacturing cost. Therefore, in such the heat treatment unit 500 as described above, a temperature sensor such as a thermocouple is inserted within the heat treatment table 501, temperature control is carried out based on the temperature detected thereby.
However, the temperature distribution of the heat treatment table is not necessarily uniform, thus correct detection of the temperature is difficult. To be correct, the temperatures are required to be measured directly of the respective parts by disposing a plurality of heaters and temperature sensors for the respective parts. However, since many temperature sensors are necessary, there are such problems that the (manufacturing cost of the apparatus goes up and the structure of the apparatus becomes complicated.
In addition, in such the conventional heat treatment unit 500 as described above, in order to heat enough the gas between the upper surface of the heat treatment table 501 and the lower surface of the wafer W, the temperature of the heat treatment table 501 is required to be heated higher than the treatment temperature of the wafer W.
However, heat transmission from the heat treatment table 501 to the wafer W is not uniform, accordingly the heat tends to linger above the center of the wafer W, affecting a higher temperature there than the surroundings.
As the result, the heat treatment becomes nonuniform, the quality of the semiconductor elements formed on the wafer W tends to fluctuate, thereby produces problems that the yield of the semiconductor elements becomes low and the manufacturing cost of the semiconductor elements goes up.
The present invention was made to solve such problems. The objective of the present invention is to provide a heat treatment apparatus which is capable of implementing a uniform heat treatment all over the whole wafer W.
Another objective of the present invention is to provide a heat treatment apparatus which is capable of carrying out an accurate temperature control during the heat treatment of the wafer W.